We learned the staggering number t, amazon.Com where so many of us shopping online, changing prices on items two and a half million times a day. When should you buy? Is it possible to lock in the best deal? We asked aditi roy to find out. Reporter: With just 11 days to go before those gifts are wrapped and under the tree, many of us are still hunting for the best online deal s. Blink and you might miss them. New analysis shows that amazon.Com changes prices an eye-popping two and a half million times a day. Walmart and best buy change prices more than 50,000 times during the month of november. Consumers are not getting the best deal. Reporter: We tried the tracking app keepa, and found this watch was $750 at 5:58 p.M. On friday at amazon. And two minutes later, the price plummeted to $510. And hours later, it was $418. Some say the best time to buy is the middle of the night. But apps like camelcamelcamel.Com and the tractor can help you nab a great price. I found this samsung galaxy notebook. Earlier in the week, it was $180, now it's down to $162. I set up a price tracker to alert me. Another tip, cancel the order right before you place it. Chances are that same retailer will e-mail you a better deal on that same gift. While you're finishing up the online shopping cart, download one of the pricing apps to your smartphone. It could save you a lot of guesswork and money.

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